This is a prospective, experimental study designed to understand the role that social stress plays in disease progress in AIDS. AIDS is a disease that is accompanied by a considerable amount of socially-induced stress, resulting in part from major disruptions in social networks. The degree to which individuals experience such socially-induced stress has been proposed as one factor contributing to the enormous variability in disease progression among HIV-infected people. Our research has focused on examining the impact of social stress on immune and endocrine function and disease progression in SIV-infected rhesus monkeys. Eighteen rhesus macaques were inoculated with SIVmac251 and 18 served as uninoculated controls. Half of each group experiences stable social conditions, and half experiences unstable social conditions. Animals are placed together daily for two hour periods in their respective social groups. To date, we have demonstrated that 1) social stability is associated with more affiliative and less agonistic behavior than is social instability; 2) social stability is associated with higher basal plasma cortisol levels compared to social instability; 3) receipt of agonistic behavior in the social conditions is associated with a lower SIV-specific IgG response; and 4) social instability is associated with faster SIV-disease progression compared to social stability. Together these results suggest social stress influences immunodeficiency disease progress, and the mechanism may involve pituitary-adrenal hormones. *KEY* SIV, AIDS, Psychosocial, Stress